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From: Like Xu <like.xu.linux@gmail.com>
To: Xiaoyao Li <xiaoyao.li@intel.com>,
	"Alexander Shishkin (hwtracing + intel_th + stm + R:perf)" 
	<alexander.shishkin@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH 3/5] KVM: VMX: RTIT_CTL_BRANCH_EN has no dependency on other CPUID bit
Date: Wed, 25 Aug 2021 11:30:49 +0800	[thread overview]
Message-ID: <711265db-f634-36ac-40d2-c09cea825df6@gmail.com> (raw)
In-Reply-To: <20210824110743.531127-4-xiaoyao.li@intel.com>

+Alexander

On 24/8/2021 7:07 pm, Xiaoyao Li wrote:
> Per Intel SDM, RTIT_CTL_BRANCH_EN bit has no dependency on any CPUID
> leaf 0x14.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>   arch/x86/kvm/vmx/vmx.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 7ed96c460661..4a70a6d2f442 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7116,7 +7116,8 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
>   
>   	/* Initialize and clear the no dependency bits */
>   	vmx->pt_desc.ctl_bitmask = ~(RTIT_CTL_TRACEEN | RTIT_CTL_OS |
> -			RTIT_CTL_USR | RTIT_CTL_TSC_EN | RTIT_CTL_DISRETC);
> +			RTIT_CTL_USR | RTIT_CTL_TSC_EN | RTIT_CTL_DISRETC |
> +			RTIT_CTL_BRANCH_EN);
>   
>   	/*
>   	 * If CPUID.(EAX=14H,ECX=0):EBX[0]=1 CR3Filter can be set otherwise
> @@ -7134,12 +7135,11 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
>   				RTIT_CTL_CYC_THRESH | RTIT_CTL_PSB_FREQ);
>   
>   	/*
> -	 * If CPUID.(EAX=14H,ECX=0):EBX[3]=1 MTCEn BranchEn and
> -	 * MTCFreq can be set
> +	 * If CPUID.(EAX=14H,ECX=0):EBX[3]=1 MTCEn and MTCFreq can be set

If CPUID.(EAX=14H,ECX=0):EBX[3]=1,

	"indicates support of MTC timing packet and suppression of COFI-based packets."

Per 31.2.5.4 Branch Enable (BranchEn),

	"If BranchEn is not set, then relevant COFI packets (TNT, TIP*, FUP, MODE.*) 
are suppressed."

I think if the COFI capability is suppressed, the software can't set the 
BranchEn bit, right ?

>   	 */
>   	if (intel_pt_validate_cap(vmx->pt_desc.caps, PT_CAP_mtc))
>   		vmx->pt_desc.ctl_bitmask &= ~(RTIT_CTL_MTC_EN |
> -				RTIT_CTL_BRANCH_EN | RTIT_CTL_MTC_RANGE);
> +					      RTIT_CTL_MTC_RANGE);
>   
>   	/* If CPUID.(EAX=14H,ECX=0):EBX[4]=1 FUPonPTW and PTWEn can be set */
>   	if (intel_pt_validate_cap(vmx->pt_desc.caps, PT_CAP_ptwrite))
> 

  reply	other threads:[~2021-08-25  3:31 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-24 11:07 [PATCH 0/5] KVM: VMX: PT (processor trace) optimizations and fixes Xiaoyao Li
2021-08-24 11:07 ` [PATCH 1/5] KVM: VMX: Restore host's MSR_IA32_RTIT_CTL when it's not zero Xiaoyao Li
2021-08-24 17:54   ` Sean Christopherson
2021-08-24 11:07 ` [PATCH 2/5] KVM: VMX: Use cached vmx->pt_desc.addr_range Xiaoyao Li
2021-08-24 15:24   ` Sean Christopherson
2021-08-24 15:42     ` Xiaoyao Li
2021-08-24 11:07 ` [PATCH 3/5] KVM: VMX: RTIT_CTL_BRANCH_EN has no dependency on other CPUID bit Xiaoyao Li
2021-08-25  3:30   ` Like Xu [this message]
2021-08-25  4:19     ` Xiaoyao Li
2021-08-25  6:08       ` Like Xu
2021-08-25  6:33         ` Xiaoyao Li
2021-08-25  8:14           ` Like Xu
2021-08-25  8:58             ` Xiaoyao Li
2021-08-25 11:53           ` Alexander Shishkin
2021-08-24 11:07 ` [PATCH 4/5] KVM: VMX: Disallow PT MSRs accessing if PT is not exposed to guest Xiaoyao Li
2021-08-24 14:20   ` Sean Christopherson
2021-08-24 15:35     ` Xiaoyao Li
2021-08-24 16:48       ` Sean Christopherson
2021-08-24 11:07 ` [PATCH 5/5] KVM: VMX: Check Intel PT related CPUID leaves Xiaoyao Li

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